Steam turbines extract work from a flow of steam to generate power. A typical steam turbine may include a rotor associated with a number of wheels. The wheels may be spaced apart from each other along the length of the rotor and define a series of turbine stages. The turbine stages are designed to extract useful work from the steam traveling on a flow path from an entrance to an exit of the turbine in an efficient manner. As the steam travels along the flow path, the steam causes the wheels to drive the rotor. The steam gradually may expand and the temperature and pressure of the steam gradually may decrease. The steam then may be exhausted from the exit of the turbine for reuse or otherwise. Higher temperature steam turbines may generate increased output as the increased temperature of the steam increases the overall energy available for extraction.
Generally described, a typical steam turbine may include a high pressure section, an intermediate pressure section, and a low pressure section. The sections may be arranged in series with each section including any number of stages. Within the sections, work is extracted from the steam to drive the rotor. Between the sections, the steam may be reheated for performing work in the next section. The high pressure and the intermediate pressure sections may operate at relatively high temperatures so as to increase the overall steam turbine output.
Although most of the flow of steam performs work in the steam turbine by flowing through the stages as described above, a portion of the flow of steam may be lost due to leakage. The steam in the leakage flow does not rotate the rotor or perform useful work. Leakage steam thus represents a loss of rotor torque and overall steam turbine output and efficiency.
Sealing members may be used in the steam turbine to reduce the leakage flow. Overall rotor torque thus may be increased by reducing the amount of the leakage flow. An example of a sealing member is an end packing head. The end packing head may be positioned near end portions of a pressurized section of the steam turbine. For example, one end packing head may be disposed over a portion of the rotor at an upstream side of a first stage bucket. The end packing head may be configured to reduce an amount of steam flowing between the end packing head and the rotor in a direction away from the first stage bucket. A measurable amount of leakage steam, however, still may pass between the rotor and the end packing head.
There is therefore a desire for improved systems and methods for cooling the wheel spaces of high temperature sections and reducing leakage steam, particularly in the case of leakage steam that has not performed useful work. Such improved systems and methods should improve overall system efficiency and output.